The long-term objective of this proposal is to understand the mechanisms underlying naturally occurring synapse elimination at neuromuscular junctions. A number of recent lines of evidence indicate surprisingly, that changes in the postsynaptic components of the neuromuscular junction may instigate the removal of the nerve terminal. Understanding how these postsynaptic changes occur is thus critical in dissecting the signal cascade during synaptic competition. The particular aim of this fellowship is to allow me to develop a new in vitro muscle preparation permitting, for the first time, long-term high resolution studies of the postsynaptic apparatus as it undergoes changes associated with synapse elimination. Quantitative optical approaches using computer assisted imaging, photobleaching, double fluorescence labeling and focal stimulation will be directed to aspects of junctional AChR dynamics such as turnover rate, lateral mobility, internalization, and eliciting activity dependent changes in AChR distribution. Our hope is that these studies will be useful for understanding this ubiquitous, but still poorly understood, phenomenon of normal development. Also, we hope this study will provide insights into analogous events and their derangements in the central nervous systems responsible for life long changes in synaptic circuitry, as occur, for example, during developmental learning and memory formation.